[R] tests for NULL objects

[Benilton Carvalho]

On Nov 29, 2006, at 7:54 PM, Martin Morgan wrote:

>> http://en.wikipedia.org/wiki/Empty_set
>> which says, in part:
>> Operations on the empty set
>
<...>
> 'any' is like 'sum', 'all' is like 'prod'.
>
> Martin

Thank you very much Martin.

It's clear now.

Benilton